This invention relates to a naphthalene carboxylic acid which is useful as starting materials for producing a liquid crystal monomer or polymer. This invention also relates to naphthalene compounds for preparing the naphthalene carboxylic acid. Liquid crystal polymers are classified into two types, that is a lyotropic liquid crystal and thermotropic liquid crystal. Recently attention has been drawn to the thermotropic liquid crystal polyester (hereinunder referred to as LCP), because it has excellent flowability and high strength. (Refer to "Plastics", Vol. 3, No. 1, pp. 156-163.) In particular, aromatic LCPs prepared from aromatic carboxylic acids have high strength and good thermal resistance.
In the prior art, aromatic hydroxy carboxylic acids such as p-hydroxy benzoic acid, 2,6-hydroxy naphthoic acid or p-hydroxy biphenyl carboxylic acid and dicarboxylic acids such as terephthalic acid, p-biphenyl dicarboxylic acid or 2,6-naphthalene dicarboxylic acid have been used for synthesizing the aromatic LCPs.
Para-hydroxy benzoic acid and p-hydroxy biphenyl carboxylic acid have been used for preparing liquid crystal monomers. The liquid crystal monomers are used as a starting material for liquid crystal having great dielectric characteristics.
Though the prior aromatic LCPs have high strength and excellent thermal resistance, the melting point of the LCPs is high and the molding properties thereof are poor.
LCPs are used in small and thin-walled electrical and electronic parts. Therefore, development of LCPs having excellent molding properties has been demanded.